Optical module

ABSTRACT

An optical module has at least two optical elements mounted in parallel with each other. The module also has a first electrode pad which is formed between the paralleled optical elements and grounded to a ground potential and a second electrode pad which is arranged along a line that is intersected with a direction in which the optical elements are arranged, which faces the first electrode pad and is grounded to the ground potential. The module further has a conductive shield member which is connected to the first electrode pad and the second electrode pad and placed between electrical signal transmission paths each connected to the optical elements.

CROSS REFERENCE TO RELATED APPLICATION

This application is a reissue of U.S. Pat. No. 7,454,104, which issuedfrom U.S. patent application Ser. No. 11/456,730, filed Jul. 11, 2006.The present inventionapplication contains subject matter related toJapanese Patent Application JP 2005-209022 filed in the Japanese PatentOffice on Jul. 19, 2005, to which priority is claimed and the entirecontents of which beingare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical module on which at least twooptical elements are mounted.

2. Description of Related Art

For an optical transmitter module for transmitting an a optical signalor an optical transmitter/receiver module for transmitting/receiving anoptical signal, a technology has been proposed for mounting pluraloptical elements on the same substrate. As a processing speed of atransmission signal by the optical module increases, a crosstalk suchthat electromagnetic radiation generated from one of optical elementsspreads to the other elements to interfere them may occur at the opticalmodule.

A technology has been proposed to increase a distance between theseelements to electrically reduce the crosstalk between the opticalelements. For an optical transmitter module, a technology has beenproposed to increase a distance between light-emitting elements (seearticle, “10 Gbps×4ch Parallel LD Module” by ANAGURA Masato, conferenceof Electronics Society in Institute of Electronics, Information andCommunication Engineers, C-3-50, p. 160, 2001).

FIG. 1 shows a configuration of an optical transmitter module as relatedart, which has been disclosed in the article. The optical transmittermodule 101A has an optical waveguide 102A in which cores 104A as curvedwaveguides and light-emitting elements 103 that are apart from eachother. Increasing a distance between the adjacent light-emittingelements enables to be reduced a crosstalk between the elements. It isto be noted that a pitch between the light-emitting elements 103 is setto 1 mm.

Further, for an optical transmitter/receiver module, a technology hasbeen proposed to increase a distance between a light-emitting elementand a light-receiving element (see Japanese Patent ApplicationPublication No. Hei 10-307238).

FIG. 2 shows a configuration of an optical a transmitter/receiver moduleas related art, which has been disclosed in the patent publication. Theoptical transmitter/receiver module 101B has an optical waveguide 102B,a light-emitting element 103, and a light-receiving element 105. Theoptical waveguide 102B includes a branching core 104B and also has, onits end face, a reflecting mirror 106 to fold back its optical path.

In an optical transmitter/receiver module, electromagnetic radiationgenerated on the side of a light-emitting element spreads to alight-receiving element to interfere it, which is then subject to anysignificant crosstalk on an electrical signal due to signal light. Thus,the optical transmitter/receiver module is more sensitive to thecrosstalk than the optical transmitter module.

If the optical transmitter/receiver module has such a configuration thata light-emitting element and a light-receiving element that are parallelwith each other are separated to an extent as to eliminate an influenceof crosstalk, the curved waveguide becomes very long to increase itscurvature, so that a module becomes very large. Therefore, in theoptical transmitter/receiver module 101B as shown in FIG. 2, thelight-emitting element 103 and the light-receiving element 105 areseparated from each other so that the reflecting mirror 106 is providedon an end face of the waveguide 102B to fold back its optical path,thereby arranging these elements at the opposite ends of the opticalwaveguide 102B.

SUMMARY OF THE INVENTION

In a configuration as shown in FIG. 1 such that the optical elements areparallel arranged to separate from each other by an increased distancebetween them in order to reduce the crosstalk, this increased distancereduces a curvature of a curved waveguide, thus increasing a loss.Therefore, in order to increase the distance between the elements whilereducing the loss, it is necessary for a waveguide to elongate, therebyresulting in a large size of the module.

Thus, crosstalk may be insufficiently reduced only by increasing adistance between the optical elements, so that additional measures maybe taken against crosstalk.

Moreover, in a configuration as shown in FIG. 2 such that an opticalpath is folded back to reduce a crosstalk, the reflecting mirror isarranged on the optical path, thereby decreasing an intensity of anoptical signal. Further, to reduce the crosstalk sufficiently, it isagain necessary to increase a distance between the optical elements,thus resulting in an increased size of a module. Moreover, there is onlya small degree of freedom in positions where the optical elements are tobe mounted, thus bringing about limitations on design of a circuitsubstrate for driving the optical elements.

It is desirable to provide an optical module that can reduce thecrosstalk without resulting in a large size of the module.

According to an embodiment of the invention, there is provided anoptical module. The optical module has at least two optical elementsmounted in parallel with each other, a first electrode pad which isformed between the paralleled optical elements and grounded to a groundpotential and a second electrode pad which is arranged along a line thatis intersected with a direction in which the optical elements arearranged, which faces the first electrode pad and grounded to the groundpotential; and a conductive shield member which is connected to thefirst electrode pad and the second electrode pad and placed betweenelectrical signal transmission paths each connected to the opticalelements.

According to an optical module of an embodiment of the presentinvention, when optical elements are driven, electromagnetic radiationoccurs along an electrical signal transmission path connected to theoptical elements. Electromagnetic radiation occurred at one of theoptical elements does not spread to the electrical signal transmissionpath of any other optical elements since this electromagnetic radiationis coupled to the shield member that is arranged between the paralleloptical elements and connected to the ground potential.

According to an optical module of the embodiment of the presentinvention, electromagnetic radiation that occurred on any one of opticalelements is coupled to a grounded shield member and so does not spreadto an electrical signal transmission path of any other optical elements,thereby enabling crosstalk between the elements to be reduced.

Further, even if the parallel optical elements are brought closer toeach other, crosstalk between the elements can be reduced, therebydecrease a size of an optical module and increasing a degree of freedomin arrangement of the optical elements. This mitigates restrictions onan electric circuit configuration to realize a simple module structurewith less crosstalk.

The concluding portion of this specification a particularly points outand directly claims the subject matter of the present invention.However, those skilled in the art will best understand both theorganization and method of operation of the invention, together withfurther advantages and objects thereof, by reading the remainingportions of the specification in view of the accompanying drawing(s)wherein like reference characters refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for showing a configuration of an opticaltransmitter module as related art;

FIG. 2 is a diagram for showing a configuration of an opticaltransmitter/receiver module as related art;

FIG. 3A is a plane view of an optical module as a first embodiment ofthe invention, for showing a configuration thereof, and FIGS. 3B and 3Care cross-sectional views thereof taken along lines IIIB-IIIB,IIIC-IIIC, respectively, shown in FIG. 3A;

FIGS. 4A and 4B are graphs for showing results of measuring alight-receiving sensitivity owing to whether or not crosstalk preventionmeasures according to embodiments of the present invention are taken;

FIG. 5A is a plane view of an optical module as a second embodiment ofthe invention, for showing a configuration thereof, and FIG. 5B is across-sectional view thereof taken along a line VB-VB shown in FIG. 5A;and

FIG. 6A is a plane view of an optical module as a third embodiment ofthe invention, for showing a configuration thereof, and FIG. 6B is across-sectional view thereof taken along a line VIB-VIB shown in FIG.6A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of an optical module ofpreferred embodiments of the present invention with reference todrawings.

Configuration of Optical Module according to a First Embodiment

FIGS. 3A-3B are diagrams of a configuration of an optical moduleaccording to the first embodiment. FIG. 3A is a plane view of theoptical module as a first embodiment of the invention, FIG. 3B is across-sectional view thereof taken along a line IIIB-IIIB shown in FIG.3A, and FIG. 3C is a sectional view thereof taken along a line IIIC-IIICshown in FIG. 3A.

The optical module 1A of the first embodiment has an optical waveguidesheet 2A having a core/clad structure, a mounting substrate 3A on whichthe optical waveguide sheet 2A is mounted, and a surface-typelight-emitting element 4 such as Vertical Cavity-Surface Emitting Laser(VCSEL) and a surface-type light-receiving element 5 such as Photo Diode(PD) that are mounted on the mounting substrate 3A.

The optical waveguide sheet 2A is one example of optical signaltransmission device and made of, for example, a polymer material. Theoptical waveguide sheet 2A has two straight cores 6A1 and 6A2 extendingroughly parallel with each other and a clad 7 that covers the cores 6A1and 6A2. The light sheet 2A is configured in such a manner that arefractive index of each of the cores 6A1 and 6A2 may be slightly largerthan that of the clad 7. This causes light coupled to the cores 6A1 and6A2 to propagate therethrough with it being confined therein.

The optical waveguide sheet 2A has an inclined end face 8 formed on oneside thereof that intersects the cores 6A1 and 6A2. The inclined endface 8 is an oblique plane having an inclination of about 45 degreeswith respect to a plane of the optical waveguide sheet 2A, wherein endfaces of the cores 6A1 and 6A2 are exposed to form reflecting faces 6a.The reflecting face 6a is formed by exposing the end face of any one ofthe cores 6A1 and 6A2 to the same plane as the inclined end face 8 andhas an inclination of about 45 degrees with respect to an extendingdirection of the cores 6A1 and 6A2.

Accordingly, light made incident upon a surface of the optical waveguidesheet 2A is reflected by the reflecting face 6a and coupled with thecore 6A1 to propagate therethrough and light propagating through thecore 6A2 is reflected by the reflecting face 6a and is then emitted fromthe optical waveguide sheet 2A roughly perpendicularly with respect to asurface of the optical waveguide sheet 2A.

The optical waveguide sheet 2A is directly adhered and fixed to asurface of the mounting substrate 3A. The mounting substrate 3A is madeof, for example, silicon (Si) and has an element-mounting concaveportion 9A where the surface-type light-emitting element 4 and thesurface-type light-receiving element 5 are mounted. The element-mountingconcave portion 9A is formed by concaving a part of a surface of themounting substrate 3A by utilizing anisotropic etching.

The two element-mounting concave portions 9A, 9A are formed at positionsthat face the reflecting faces 6a, 6a of the cores 6A1, 6A2 in theoptical waveguide sheet 2A mounted on the surface of the mountingsubstrate 3A. In this embodiment, two element-mounting concave portions9A, 9A are parallel with each other at places pulled in from a rear endof the mounting substrate 3A.

One of the element-mounting concave portions 9A is configured to have anopening large enough to contain the surface-type light-emitting element4 and a depth a little deeper than its height in order to mount thesurface-type light-emitting element 4 thereon. The otherelement-mounting concave portion 9A is configured to have an openinglarge enough to contain the surface-type light-receiving element 5 and adepth a little deeper than its height in order to mount the surface-typelight-receiving element 5 thereon.

The mounting substrate 3A has insulation films 10, 10, which is made ofsilicon oxide (SiO2), formed on its right side and back side and alsohas an element-mounting bonding pad 11A formed on each of theelement-mounting concave portions 9A, 9A. On the mounting substrate 3A,the surface-type light-emitting element 4 is mounted in one of theelement-mounting concave portions 9A, 9A on which the bonding pad 11A isformed and the surface-type light-receiving element 5 is mounted in theother element-mounting concave portion 9A on which the bonding pad 11Ais formed.

The surface-type light-emitting element 4 and the surface-typelight-receiving element 5 are each one example of an optical element.The surface-type light-emitting element 4 has a light-emitting portion4a that emits light. The surface-type light-emitting element 4 ismounted on the element-mounting concave portion 9A at a position thatthe light-emitting portion 4a faces the reflecting face 6a of the core6A1 of the optical waveguide sheet 2A. Accordingly, the surface-typelight-emitting element 4 is optically coupled with the core 6A1 of thelight guide 2A via the reflecting face 6a.

The surface-type light-receiving element 5 has a light-receiving portion5a to which light is made incident upon. The surface-typelight-receiving element 5 is mounted on the other element-mountingconcave portion 9A at a position that the light-receiving portion 5afaces the reflecting face 6a of the core 6A2 of the optical waveguidesheet 2A. Accordingly, the surface-type light-receiving element 5 isoptically coupled with the core 6A2 of the light guide 2A via thereflecting face 6a.

Then, the surface-type light-emitting element 4 and the surface-typelight-receiving element 5 are fixed to the bonding pad 11A by using aconductive adhesive agent or through soldering so that a back-surfaceelectrode, not shown, of each of the surface-type light-emitting element4 and the surface-type light-receiving element 5 may be electricallyconnected to the bonding pad 11A.

On a surface of the mounting substrate 3A, a first ground potentialelectrode pad 12 is formed between the element-mounting concave portions9A, 9A. The first ground potential electrode pad 12 is one example of afirst electrode pad and has such a shape as to extend from a positionbetween the element-mounting concave portions 9A, 9A to the read end ofthe mounting substrate 3A. It is to be noted that the first groundpotential electrode pad 12 and each of the bonding pads 11A can bemanufactured on the surface of the mounting substrate 3A by the samestep.

The mounting substrate 3A has a grounding electrode 13 formed all overthe back surface, so that the first ground potential electrode pad 12formed on the surface of the mounting substrate 3A and the groundingelectrode 13 formed on the back surface of the mounting substrate 3A areelectrically connected to each other through a conducting electrode 14Aformed at the rear end of the mounting substrate 3A. The conductingelectrode 14A is constituted of an electrode pattern formed on the endsurface on a side of the rear end of the mounting substrate 3A and hasits upper side connected to the first ground potential electrode pad 12and its lower end connected to the grounding electrode 13.

The mounting substrate 3A mounting the optical waveguide sheet 2A, thesurface-type light-emitting element 4 and the surface-typelight-receiving element 5 is then installed on an electric circuitsubstrate 15.

The electric circuit substrate 15 has a circuit substrate groundpotential electrode pad 16 formed on its surface. The circuit substrateground potential electrode pad 16 is one example of a ground electrodeand has at least the same size as the grounding electrode 13 formed allover the back surface of the mounting substrate 3A and is grounded (GND)through a bonding wire etc., which are not shown.

The mounting substrate 3A is placed on the circuit substrate groundpotential electrode pad 16 on the electric circuit substrate 15 andfixed thereto by using a conductive adhesive or through soldering, sothat the grounding electrode 13 of the mounting substrate 3A and thecircuit substrate ground potential electrode pad 16 of the electriccircuit substrate 15 are electrically connected to each other.

As described above, the first ground potential electrode pad 12 on themounting substrate 3A is electrically connected to the groundingelectrode 13. The grounding electrode 13 is formed all over the backsurface of the mounting substrate 3A so as to be in contact with thecircuit substrate ground potential electrode pad 16 all over a backsurface thereof.

According to such a configuration, the first ground potential electrodepad 12 is connected to the circuit substrate ground potential electrodepad 16 on the electric circuit substrate 15 through a large area.Accordingly, the first ground potential electrode pad 12 has nofrequency dependency and functions as a good ground pad at a highfrequency too.

On the electric circuit substrate 15, adjacent to the mounting substrate3A, a driver integrated circuit (IC) 17 is mounted behind thesurface-type light-emitting element 4 and a receiver IC 18 is mountedbehind the surface-type light-receiving element 5.

The surface-type light-emitting element 4 and the driver IC 17 areconnected to each other in such a manner that an electrode pad 4b on thesurface of the surface-type light-emitting element 4 and the bonding pad11A connected with a back surface electrode, not shown, of thesurface-type light-receiving element 4 are connected to an electrode pad17a on a surface of the driver IC 17 through a bonding wire 19. Thebonding wire 19 is one example of an electrical signal transmission pathand made of, for example, gold (Au) and connected to the surface-typelight-emitting element 4 and the driver IC 17 by wire bonding.

Similarly, the surface-type light-receiving element 5 and the receiverIC 18 are connected to each other in such a manner that an electrode pad5b on the surface of the surface-type light-receiving element 5 and thebonding pad 11A connected with a back surface electrode, not shown, ofthe surface-type light-receiving element 5 are connected to an electrodepad 18a on the surface of the receiver IC 18 through the bonding wire19.

The electric circuit substrate 15 has a second ground potentialelectrode pad 20 formed on it independently of the circuit substrateground potential electrode pad 16. The second ground potential electrodepad 20 is one example of a second electrode pad and formed at a positionthat faces the first ground potential electrode pad 12 in such adirection as to intersect with a direction in which the surface-typelight-emitting element 4 and the surface-type light-receiving element 5are arranged. In the present embodiment, the second ground potentialelectrode pad 20 is formed on a position between the driver IC 17 andthe receiver IC 18 on the surface of the electric circuit substrate 15and grounded through a bonding wire etc.

The first ground potential electrode pad 12 on the mounting substrate 3Aand the second ground potential electrode 20 on the electric circuitsubstrate 15 are connected to each other by a bonding wire 21. Thebonding wire 21 is one example of a shield member and is made, forexample, gold (Au) and has its one end connected to the first groundpotential electrode pad 12 and the other end thereof connected to thesecond ground potential electrode pad 20. The first ground potentialelectrode pad 12 is grounded through the grounding electrode 13 and thecircuit substrate ground potential electrode pad 16 and the secondground potential electrode pad 20 is also grounded, so that the bondingwire 21 is connected to the ground potential.

The bonding wire 21 is stretched at almost the same height as thebonding wire 19 that connects the surface-type light-emitting element 4and the driver IC 17 and the surface-type light-receiving element 5 andthe receiver IC 18. Further, although the number of the bonding wires 21may be singular, the number thereof may be plural; in the presentembodiment, the three bonding wires 21 are stretched roughly parallelwith each other.

Example of Operations of Optical Module of First Embodiment

The following will describe an example of operations of the opticalmodule of the first embodiment. An electrical signal output from thedriver IC 17 passes through the bonding wire 19 and enters thesurface-type light-emitting element 4 where an electrical signal isconverted into an optical signal and issued therefrom.

The optical signal is emitted from the surface-type light-emittingelement 4 roughly perpendicularly to the mounting substrate 3A andenters the optical waveguide sheet 2A through its lower surface. Theoptical signal made incident upon the lower surface of the opticalwaveguide sheet 2A roughly perpendicularly is reflected by thereflecting face 6a and coupled with one of the cores 6A1 to propagatethrough it.

In contrast, another optical signal propagating through the other core6A2 is reflected by the reflecting face 6a and issued from the lowersurface of the optical waveguide sheet 2A roughly perpendicularly. Theoptical signal issued roughly perpendicularly from the lower surface ofthe optical waveguide sheet 2A is made incident upon the surface-typelight-receiving element 5 to be converted into an electrical signal. Theelectrical signal output from the surface-type light-receiving element 5passes through the bonding wire 19 to enter the receiver IC 18.

Accordingly, the optical module 1A constitutes a paralleltransmitter/receiver module that has a function to transmit an opticalsignal emitted from the surface-type light-emitting element 4 throughthe core 6A1 of the optical waveguide sheet 2A and has a function toreceive an optical signal from the other core 6A2 by using thesurface-type light-receiving element 5.

The optical module 1A thus having a light-emitting element and alight-receiving element, for example, the surface-type light-emittingelement 4 and the surface-type light-receiving element 5 encounterselectromagnetic radiation generated from the bonding wire 19 when anelectrical signal that drives the surface-type light-emitting element 4is sent from the driver IC 17 to the surface-type light-emitting element4 via the bonding wire 19. In a related optical module, electromagneticradiation generated from the transmission-side bonding wire 19connecting the surface-type light-emitting element 4 and the driver IC17 to each other has been coupled with the reception-side bonding wireconnecting the light-receiving element and the receiver IC to eachother, thus resulting in a crosstalk.

In contrast, in the optical module 1A of the present embodiment, bystretching the bonding wire 21 connected to the ground potential betweenthe transmission-side bonding wire 19 and the reception-side bondingwire 19, electromagnetic radiation generated from the transmission-sidebonding wire 19 is coupled with the bonding wire 21 stretched betweenthe transmissions-side bonding wire 19 and the reception-side bondingwire 19.

Accordingly, electromagnetic radiation generated by thetransmission-side bonding wire 19 is not propagated to thereception-side bonding wire 19 to reduce the crosstalk. Further, thebonding wire 21 is connected to the ground potential, so that thecoupled electromagnetic radiation has no influence on the surface-typelight-receiving element 5 or the receiver IC 18.

To efficiently couple the electromagnetic radiation generated from thetransmission-side bonding wire 19 and propagated to the reception-sidebonding wire 19 with the bonding wire 21, this wire 21 is stretched atalmost the same height as the transmission-side and reception-sidebinding wires 19 by aligning it in height with respect to thetransmission-side and reception-side binding wires 19 and thecross-talk-reducing bonding wire 21.

The larger the number of the bonding wires 21 is, the higher the effectsof reducing crosstalk become; in fact, in the present embodiment, thethree bonding wires 21 are stretched in consideration of sizes of thefirst ground potential electrode pad 12 and the second ground potentialelectrode pad 20, workability of wire bonding, etc.

FIGS. 4A and 4B are graphs showing a result of measuring alight-receiving sensitivity owing to whether crosstalk preventionmeasures of the embodiment of the present invention are taken, whichresult was obtained by checking effects of the embodiment of the presentinvention by using an optical transmitter/receiver module in which asurface-type light-emitting element and a surface-type light-receivingelement were arranged in parallel with each other.

FIG. 4A shows a result of measuring a bit error ratio (BER) of areception system when the surface-type light-emitting element was driven(VCSEL ON) and when it was not driven (VCSEL OFF) in a case wherecrosstalk prevention measures according to the embodiment of the presentinvention were taken. FIG. 4B shows, for comparison, a result ofmeasurement in a case where the crosstalk prevention measures of theembodiment of the present invention were not taken.

In the case where the crosstalk prevention measures were not taken, alight reception sensitivity of BER<10⁻¹² deteriorated by about 3 dB whenthe surface-type light-emitting element was driven. In contrast, bytaking the crosstalk prevention measures of the embodiment of thepresent invention, the light reception sensitivity deteriorated by 0.5dB when the surface-type light-emitting element was driven, confirmingan effect of reducing the crosstalk by about 2.5 dB.

As described above, in the optical module 1A of the first embodiment, bystretching the bonding wire 21 connected to the ground potential betweenthe surface-type light-emitting element 4 and the surface-typelight-receiving element 5, crosstalk between the elements can bereduced. Accordingly, even if the surface-type light-emitting element 4and the surface-type light-receiving element 5 arranged in parallel witheach other are brought closer to each other, crosstalk between theseelements can be reduced, thereby miniaturizing the optical module. Forexample, even if a distance between the surface-type light-emittingelement 4 and the surface-type light-receiving element 5 is decreased toabout 600 μm, crosstalk between them can be reduced.

Further, a degree of freedom of arrangement of the surface-typelight-emitting element 4 and the surface-type light-receiving element 5is increased, so that limitations on an electric circuit configurationetc. are also mitigated.

Moreover, the first ground potential electrode pad 12 which is formed onthe surface of the mounting substrate 3A and to which thecrosstalk-reducing bonding wire 21 is connected is connected to thegrounding electrode 13 formed on the back surface of the mountingsubstrate 3A by forming the conducting electrode 14A at the rear end ofthe mounting substrate 3A, so that the first ground potential electrodepad 12 is connected with the circuit substrate ground potentialelectrode pad 16 on the electric circuit substrate 15 in a large area.

Thus, the first ground potential electrode pad 12 on the surface of themounting substrate 3A can function as a good ground pad having nofrequency dependency at a high frequency too, so that electromagneticradiation is coupled with the bonding wire 21 to improve an effect ofreducing the crosstalk.

Configuration Example of Optical Module of Second Embodiment

FIGS. 5A and 5B show a configuration of an optical module of the secondembodiment of the invention. FIG. 5A is a plan view of the opticalmodule 1B and FIG. 5B is a cross-sectional view taken along a line VB-VBof FIG. 5A.

An optical module 1B of the second embodiment has an optical waveguidesheet 2B with a core/clad structure, a mounting substrate 3B on whichthe optical waveguide sheet 2B is mounted, and a surface-typelight-emitting element 4 and a surface-type light-receiving element 5that are mounted on the mounting substrate 3B.

In the optical module 1B of the second embodiment, the optical waveguidesheet 2B has a Y-branched core in which one core 6B spreads into twocores 6B1 and 6B2. In the optical waveguide sheet 2B, on one side thatthe branched cores 6B1 and 6B2 intersect, an inclined end face 8 isformed. The cores 6B1 and 6B2 are exposed on the inclined end face 8, toform a reflecting face 6a.

To the branched core 6B1, the surface-type light-emitting element 4 iscoupled via the reflecting face 6a, and to the branched core 6B2, thesurface-type light-receiving element 5 is coupled via the reflectingface 6a, so that an optical signal output from the surface-typelight-emitting element 5 is combined with an optical signal input to thesurface-type light-receiving element 5 into the one core 6B.Accordingly, a one-core-double type optical module is configured inwhich optical signals are transmitted/received by one optical fiber.

Further, in the optical module 1B, on the mounting substrate 3B, each ofthe element-mounting concave portions 9B, 9B on which the surface-typelight-emitting element 4 and the surface-type light-receiving element 5are mounted is formed close to a rear end of the mounting substrate 3B.In the present embodiment, the rear end of the mounting substrate 3Bintersects each of the element-mounting concave portions 9B, 9B.

Accordingly, positions on which the surface-type light-emitting element4 and the surface-type light-receiving element 5 are mounted are broughtclose to the rear end of the mounting substrate 3B. This enables adistance between the surface-type light-emitting element 4 and a driverIC 17 and a distance between the surface-type light-receiving element 5and a receiver IC 18 to be shortened.

By thus shortening the distance between the surface-type light-emittingelement 4 and the driver IC 17 and the distance between the surface-typelight-receiving element 5 and the receiver IC 18, a bonding wire 19connecting the surface-type light-emitting element 4 and the driver IC17 and another bonding wire 19 connecting the surface-typelight-receiving element 5 and the receiver IC 18 can be shortened.

This is because the bonding wire 19, if it is long, deteriorates greatlywhen a high-frequency signal is transmitted through it so that thebonding wire 19 may be preferably configured as short as possible.

Further, this is because if the bonding wire 19 is long when a signal istransmitted at a high frequency, electromagnetic radiation generated onthe transmission-side bonding wire 19 is increased, which bring aboutany increase in crosstalk due to the electromagnetic radiation so thatthe bonding wire 19 may be preferably configured as short as possible.

Moreover, in the optical module 1B, on the mounting substrate 3B,bonding pads 11B formed in the element-mounting concave portions 9B, 9Bare respectively formed so as to extend to a surface of the mountingsubstrate 3B. Then, the bonding wires 19 are connected to the bondingpads 11B on the side of the surface of the mounting substrate 3B. Withthis, a height of a position where each of the bonding wires 19 isconnected to the electrode pad is roughly equalized to each other toalign wire bonding heights, thereby improving workability of wirebonding.

As described above, in the optical module 1B, the bonding pad 11B formedin each of the element-mounting concave portions 9B, 9B is extended upto the surface of the mounting substrate 3B in such a shape that therear end of the mounting substrate 3B may intersect each of theelement-mounting concave portions 9B, 9B, so that each of the bondingpads 11B connected with the surface-type light-emitting element 4 andthe surface-type light-receiving element 5 reaches the read end of themounting substrate 3B.

Therefore, if a first ground potential electrode pad 12 formed on thesurface of the mounting substrate 3B and a grounding electrode 13 formedall over the back surface of the mounting substrate 3B are connected toeach other by forming a conducting electrode 14 on a rear end of themounting substrate as in the case of the optical module 1A of the firstembodiment, the bonding pad 11B also is connected to a ground potential.

If such a configuration is employed that the conducting electrode isformed at the rear end of the mounting substrate to make the firstground potential electrode pad 12 and the grounding electrode 13conductive to each other, in order to prevent the bonding pad 11B fromconnecting to the conducting electrode, it is necessary to mask theconducting electrode so that it disconnects the bonding pad 11B and thenform the conducting electrode on the rear end of the mounting substrate,thus resulting in an increase in numbers of steps to be performed.

Therefore, in the optical module 1B of the second embodiment, aconducting electrode 14B that connects the first ground potentialelectrode pad 12 and extends to one side end of the mounting substrate3B is formed on the surface of the mounting substrate 3B.

Then, by forming a conducting electrode 14C by sputtering or evaporationon the end face of one of the side ends of the mounting substrate 3B,the first ground potential electrode pad 12 formed on the surface of themounting substrate 3B is connected with the grounding electrode 13formed all over the back surface of the mounting substrate 3B. It is tobe noted that the first ground potential electrode pad 12 formed on thesurface of the mounting substrate 3B, the conducting electrode 14B, andthe bonding pads 11B can be manufactured by the same step.

Such a configuration makes it possible to easily connect the firstground potential electrode pad 12 on the surface side of the mountingsubstrate 3B to the ground potential of an electric circuit substrate15.

Example of Operations of Optical Module of Second Embodiment

The following will describe an example of operations of the opticalmodule of the second embodiment. An electrical signal output from thedriver IC 17 passes through the bonding wire 19 and enters thesurface-type light-emitting element 4. The surface-type light-emittingelement 4 in turn converts the electrical signal into an optical signaland emits it.

The optical signal is emitted from the surface-type light-emittingelement 4 roughly perpendicularly to the mounting substrate 3B andenters into the optical waveguide sheet 2B through its lower surface.The optical signal made incident upon the lower surface of the opticalwaveguide sheet 2B roughly perpendicularly is reflected by thereflecting face 6a and coupled to the one branched core 6B1, therebypropagating from the core 6B1 to the core 6B.

In contrast, another optical signal propagating through the other core6B2 branching from the core 6B is reflecting face 6a and issued from thelower surface of the optical waveguide sheet 2B roughly perpendicularly.This optical signal issued from the lower surface of the opticalwaveguide sheet 2B roughly perpendicularly impinges on the surface-typelight-receiving element 5 where it is converted into an electricalsignal. The electrical signal output from the surface-typelight-receiving element 5 is transferred through the bonding wire 19 tothe receiver IC 18.

Accordingly, the optical module 1B constitutes a one-core double typetransmitter/receiver module that has a function to transmit an opticalsignal from the surface-type light-emitting element 4 through the core6B of the optical waveguide sheet 2B and has a function to receive anoptical signal entered from the same core 6B by using the surface-typelight-receiving element 5.

Like the optical module 1A of the first embodiment, the optical module1B having the surface-type light-emitting element 4 and the surface-typelight-receiving element 5 generate electromagnetic radiation from thebonding wire 19 when an electrical signal that drives the surface-typelight-emitting element 4 is sent from the driver IC 17 to thesurface-type light-emitting element 4 through the bonding wire 519.

Therefore, in the optical module 1B also, by stretching the bonding wire21 connected to the ground potential between the transmission-sidebonding wire 19 and the reception-side bonding wire 19, electromagneticradiation generated by the transmission-side bonding wire 19 is coupledwith the bonding wire 21 stretched between the transmission-side and thereception-side bonding wires 19.

Accordingly, electromagnetic radiation generated by thetransmission-side bonding wire 19 does not propagate to thereception-side bonding wire 19 to reduce crosstalk. Further, the bondingwire 21 is connected to the ground potential, so that the coupledelectromagnetic radiation has no influence on the surface-typelight-receiving element 5 or the receiver IC 18.

As described above, in the optical module 1B of the second embodimentalso, by stretching the bonding wire 21 connected to the groundpotential between the surface-type light-emitting element 4 and thesurface-type light-receiving element 5, crosstalk between these elementscan be reduced to obtain the same effects as the optical module 1A ofthe first embodiment.

Further, even if the paralleled surface-type light-emitting element 4and the surface-type light-receiving element 5 are brought close to eachother, crosstalk between the elements can be reduced and a curvature canbe increased even if using a curved waveguide, thereby reducing a loss.

Moreover, the waveguide is not lengthened, so that the optical module 1Bcan be miniaturized.

Configuration of Optical Module of Third Embodiment

FIGS. 6A and 6B show a configuration of an optical module of the thirdembodiment of the invention. FIG. 6A is a plan view of the opticalmodule 1C and FIG. 6B is a cross-sectional view thereof taken along aline VIB-VIB of FIG. 6A.

In an optical module 1C of the third embodiment, a first groundpotential electrode pad 12 and a circuit substrate ground potentialelectrode pad 16 are connected to each other by a bonding wire 22instead of forming electrode patterns on an end face of a mountingsubstrate.

Supposing that the optical module 1C of the third embodiment has thesame configuration as the optical module 1B of the second embodimentexcept that the first ground potential electrode pad 12 and the circuitsubstrate ground potential electrode pad 16 are connected to each other,like reference characters refer to like elements in the secondembodiment.

In the optical module 1C of the third embodiment, the first groundpotential electrode pad 12 is formed on a surface of a mountingsubstrate 3C and a conducting electrode 14D connecting to the firstground potential electrode pad 12 is formed on the surface of themounting substrate 3C. The conducting electrode 14D extends to adirection of one of the side ends of the mounting substrate 3C to form aground pad 23 at a position where the electrode 14D is exposed from aoptical waveguide sheet 2B, thereby making the first ground potentialelectrode pad 12 and the ground pad 23 conductive to each other via theconducting electrode 14D.

The first ground potential electrode pad 12 on the mounting substrate 3Cand the circuit substrate ground potential electrode pad 16 on anelectric circuit substrate 15 are connected to each other by a bondingwire 22. The bonding wire 22 is made of, for example, gold (Au) and hasits one end connected to the ground pad 23 by wire bonding and the otherend thereof connected to the circuit substrate ground potentialelectrode pad 16.

Accordingly, the first ground potential electrode pad 12 is connected tothe ground via the bonding wire 22 and the circuit substrate groundpotential electrode pad 16. The number of the bonding wires 23 is, forexample, at least two; in the present embodiment, the four bonding wires23 are stretched substantially in parallel with each other. Although inFIG. 4, the ground pad 23 has been formed approximately at a middle ofthe mounting substrate 3C to arrange the plural bonding wires 22 closeto each other, the ground pad 23 may be formed in a length direction ofthe mounting substrate 3C to arrange the plural bonding wires 22 with aspacing therebetween in the length direction of the mounting substrate3C.

The optical module 1C of the third embodiment has such a configurationto thereby enable to be performed in the same process a step of bindinga wire between each optical element and the driver IC or the receiverIC, a step of connecting the first ground potential electrode pad 12 andthe second ground potential electrode pad 20 to each other, and a stepof connecting the ground pad 23 connected with the first groundpotential electrode pad 12 and the circuit substrate ground potentialelectrode pad 16 to each other. This enables the first ground potentialelectrode pad 12 on the surface side of the mounting substrate 3C to besimply connected to the ground potential of the electric circuitsubstrate 15.

Further, to the first ground potential electrode pad 12, acrosstalk-reducing bonding wire 21 is connected, so that by forming theground pad 23 connected via the conducting electrode 14D at a positiondifferent from a place where the first ground potential electrode pad 12is formed, the grounding bonding wire 22 is connected to the ground pad23. Accordingly, the bonding wire 22 can be connected at a positiondifferent from a position where the bonding wire 21 is connected to thefirst ground potential electrode pad 12, thereby eliminating complicatedcontrol etc. in the wire bonding step.

Example of Operations of Optical Module of Third Embodiment

The optical module 1C of the third embodiment performs the sameoperations as those of the optical module 1B of the second embodimentwhen transmitting/receiving an optical signal. In the optical module 1Cof the third embodiment, electromagnetic radiation is generated from abonding wire 19 when an electrical signal that drives a surface-typelight-emitting element 4 is sent from a driver IC 17 to the surface-typelight-emitting element 4 through the bonding wire 19.

Therefore, in the optical module 1C, by stretching a bonding wire 21connected to the ground potential between the transmission-side bondingwire 19 and the reception-side bonding wire 19, electromagneticradiation generated by the transmission-side bonding wire 19 is coupledwith the bonding wire 21 stretched between the transmission-side and thereception-side bonding wires 19.

Accordingly, electromagnetic radiation generated by thetransmission-side bonding wire 19 does not propagate to the areception-side bonding wire 19 to reduce crosstalk. Further, as thebonding wire 21 is connected to the ground potential, the coupledelectromagnetic radiation has no influence on the surface-typelight-receiving element 5 or a receiver IC 18.

As described above, in the optical module 1C of the third embodimentalso, by stretching the bonding wire 21 grounded to the ground potentialbetween the surface-type light-emitting element 4 and the surface-typelight-receiving element 5, crosstalk between these elements can bereduced to obtain the same effects as those of the optical module 1A ofthe first embodiment and the optical module 1B of the second embodiment.

Further, the first ground potential electrode pad 12 formed on themounting substrate 3C and the circuit substrate ground potentialelectrode pad 16 formed on the electric circuit substrate 15 can beconnected to each other in the same process as a step of bonding a wirebetween the optical element and the driver IC, so that the manufacturingprocess can be simplified.

Modification of Optical Module of Each Embodiment

Although the optical module 1A of the above first embodiment, theoptical module 1B of the above second embodiment, and the optical module1C of the above third embodiment have been described with reference toan example of an optical transmitter/receiver module having onelight-emitting element and one light-receiving element as opticalelements, an optical transmitter module may be employed which has nolight-receiving element but plural light-emitting elements. Further, alight-receiving module may be employed which has no light-emittingelement but plural light-receiving elements. Furthermore, an opticaltransmitter/receiver module may be employed which has plurallight-emitting elements and plural light-receiving elements. In such amanner, it is of course possible to reduce crosstalk by the sameconfiguration in a variety of embodiments of optical modules havingplural optical elements.

A core structure configuring a straight waveguide in the opticalwaveguide sheet 2A of the optical module 1A of the first embodiment maybe applied to the optical waveguide sheet 2B of the optical modules 1Band 1C of the respective second and third embodiments. Similarly, a corestructure configuring branching waveguides in the optical waveguidesheet 2B of the optical modules 1B and 1C of the respective second andthird embodiments may be applied to the optical waveguide sheet 2A ofthe optical module 1A of the first embodiment.

Although the optical modules 1A, 1B, and 1C of the embodiments haveemployed an optical waveguide sheet made of a polymer material asoptical signal propagation device, it is clear that an optical signalcan be propagated by using a light guide made of a quartz-basedmaterial, an optical fiber made of a quartz-based material, an opticalfiber made of a plastic, or a combination of these.

Although the optical modules 1A, 1B, and 1C of the embodiments haveprovided roughly the same height of the plural crosstalk-reducingbonding wires 21, the bonding wires 21 may have different heights inconsideration of a spread of electromagnetic radiation generated by thetransmission-side bonding wire 19. Further, positions where the bondingwires 21 are respectively connected with the electrode pad may beshifted in a back-and-forth direction.

Although the optical modules 1A, 1B, and 1C of the embodiments haveutilized a bonding wire as a crosstalk-reducing shield member, it may beconstituted of a thin sheet material having conductivity. However, byutilizing a bonding wire as the shield member, the crosstalk-reducingbonding wire can also be connected in the step of binding wires toelectrically connect the surface-type light-emitting element 4 and thesurface-type light-receiving element 5, to facilitate a mounting stepand enable utilizing of the existing mounting equipment, therebyreducing manufacturing costs.

The present invention is applied to an optical communication modulebetween boards or chips of an electronic device, a connector of acommunication cable utilizing an optical fiber, etc. It should beunderstood by those skilled in the art that various modifications,combinations, sub-combination and alternations may occur depending ondesign requirements and other factors insofar as they are within thescope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An optical module comprising: at least twooptical elements mounted in parallel with each other; a first electrodepad formed between the paralleled optical elements and grounded to aground potential; a second electrode pad arranged along a line that isintersected with by a direction in which the at least two opticalelements are arranged, said second electrode pad facing the firstelectrode pad, and said second electrode pad being grounded to theground potential; and a conductive shield member connected to both thefirst electrode pad and the second electrode pad and positioned betweenelectrical signal transmission paths, each one of which is connected toa respective one of the optical elements, wherein, the conductive shieldmember includes a linear wire, said linear wire having one end connectedto the first electrode pad and the other end thereof connected thesecond electrode pad, and is stretched between the first electrode padand the second electrode pad at a height aligned with a height of theelectrical signal transmission path connected to the at least twooptical elements.
 2. The optical module according to claim 1, whereinplural wires are stretched between the first electrode pad and thesecond electrode pad.
 3. The optical module according to claim 1,wherein the linear wire is made of gold and stretched between the firstelectrode pad and the second electrode pad by wire bonding.
 4. Theoptical module according to claim 1, further comprising a mountingsubstrate that mounts the optical element, the paralleled opticalelements being mounted on the mounting substrate and the first electrodepad being formed on the mounting substrate.
 5. The optical moduleaccording to claim 4, further comprising an electric circuit substrateon which the mounting substrate is mounted, wherein the second electrodepad is formed on the electric circuit substrate; and wherein the firstelectrode pad formed on the mounting substrate is connected to the aground electrode formed on the electric circuit substrate.
 6. Theoptical module according to claim 5, further comprising a groundingelectrode that is electrically connected to the first electrode pad on aback surface of the mounting substrate, wherein the grounding electrodeis mounted on the ground electrode formed on the electric circuitsubstrate, to connect the first electrode pad with the ground throughthe ground electrode and the grounding electrode.
 7. The optical moduleaccording to claim 6, wherein a conducting electrode that makes thefirst electrode pad and the grounding electrode conductive to each otheris formed on a side surface of the mounting substrate.
 8. The opticalmodule according to claim 5, wherein the first electrode pad formed onthe mounting substrate is grounded to the ground electrode formed on theelectric circuit substrate, by a conductive wire having conductivity. 9.The optical module according to claim 8, further comprising on a surfaceof the mounting substrate a grounding pad which is conductive to thefirst electrode pad and to which the conductive wire for grounding isconnected, wherein the conductive wire for grounding and the firstelectrode pad are connected to each other at a position different from aposition where the conductive shield member is connected to the firstelectrode pad.
 10. The optical module according to claim 1, furthercomprising an optical signal transmission device which has a core and aclad to couple the core and the at least two optical elements with eachother.
 11. The optical module according to claim 1, wherein one of theat least two optical elements is a light-emitting element and another ofthe at least two optical elements is a light-receiving element.
 12. Theoptical module according to claim 11, wherein: the at least two opticalelements comprise a plurality of light-emitting elements and a pluralityof light-receiving elements; the electrical signal transmission pathscomprise (a) a first electrical signal transmission path connected to atleast one of the plurality of light-emitting elements and (b) a secondelectrical signal transmission path connected to at least one of thelight-receiving elements; and the conductive shield member is disposedbetween the first electrical signal transmission path and the secondelectrical signal transmission path.
 13. The optical module according toclaim 12, wherein the conductive shield member comprises a plurality ofbonding wires.
 14. The optical module according to claim 11, wherein adistance between the light-emitting element and the light-receivingelement is 600 micrometers or more.
 15. The optical module according toclaim 11, wherein the at least one light-emitting element and the atleast one light-receiving element are arranged along a common line. 16.The optical module according to claim 11, further comprising: a driverIC that is electrically connected to at least one of the at least twooptical elements; and a receiver IC that is electrically connected to atleast one of the at least two optical elements.
 17. The optical moduleaccording to claim 11, wherein the electrical signal transmission pathscomprise: a first electrical signal transmission path connected to theat least one light-emitting element; and a second electrical signaltransmission path connected to the at least one light-receiving element.18. The optical module according to claim 17, wherein: the conductiveshield member comprises a plurality of bonding wires; and each of theplurality of bonding wires is disposed between the first electricalsignal transmission path and the second electrical signal transmissionpath.
 19. The optical module according to claim 18, wherein: each of theplurality of bonding wires is configured to shield the first electricalsignal transmission path from electromagnetic radiation from the secondelectrical signal transmission path, and each of the plurality ofbonding wires is configured to shield the second electrical signaltransmission path from electromagnetic radiation from the firstelectrical signal transmission path.
 20. The optical module according toclaim 18, wherein at least one of the plurality of bonding wires isdisposed substantially along a line that runs midway between at leastone neighboring pair of the at least two optical elements.
 21. Theoptical module according to claim 17, wherein the conductive shieldmember is disposed between the first electrical signal transmission pathand the second electrical signal transmission path.
 22. The opticalmodule according to claim 21, wherein the at least one light-emittingelement includes a Vertical Cavity-Surface Emitting Laser (VCSEL), andthe at least one light-receiving element includes a photo diode.
 23. Theoptical module according to claim 21, wherein: the conductive shieldmember is configured to shield the first electrical signal transmissionpath from electromagnetic radiation from the second electrical signaltransmission path, and the conductive shield member is configured toshield the second electrical signal transmission path fromelectromagnetic radiation from the first electrical signal transmissionpath.
 24. The optical module according to claim 21, wherein theconductive shield member is disposed substantially along a line thatruns midway between at least one neighboring pair of the at least twooptical elements.
 25. The optical module according to claim 1, whereinthe conductive shield member comprises a plurality of linear wiresconnected to the first electrode pad.
 26. The optical module accordingto claim 1, further comprising a mounting substrate and a bonding padfor at least one of the at least two optical elements, wherein thebonding pad is disposed on the mounting substrate.
 27. The opticalmodule according to claim 1, further comprising a substrate, wherein thefirst electrode pad is disposed on a surface of the substrate.
 28. Theoptical module according to claim 1, further comprising a groundelectrode and a substrate, wherein the ground electrode is disposed on aback surface of the substrate, and wherein the first electrode pad andthe ground electrode are electrically connected to one other.
 29. Theoptical module according to claim 1, further comprising a groundpotential electrode that is electrically connected to the firstelectrode pad.
 30. The optical module according to claim 1, wherein theat least two optical elements comprise a light-receiving element array.31. The optical module according to claim 1, further comprising anoptical waveguide member, wherein the optical waveguide member comprisesa core and a clad.
 32. The optical module according to claim 1, whereinthe electrical signal transmission paths are made of gold.
 33. Theoptical module according to claim 1, wherein the electrical signaltransmission paths comprise gold.
 34. The optical module according toclaim 1, wherein: the conductive shield member includes a plurality ofmetal wires, each of the plurality of metal wires including a first endand a second end; and the first end of each of the plurality of metalwires is disposed on a first surface, and the second end of each of theplurality of the metal wires is disposed on a second surface, the secondsurface being higher than the first surface.
 35. The optical moduleaccording to claim 1, further comprising a receiver IC that iselectrically connected to at least one of the at least two opticalelements.
 36. The optical module according to claim 35, furthercomprising an electric circuit support substrate, wherein: the electriccircuit support substrate has a first surface, and wherein the receiverIC and the at least one of the at least two optical elements aredisposed above the first surface.
 37. The optical module according toclaim 36, wherein the receiver IC and the at least one of the at leasttwo optical elements are electrically connected to the electric circuitsupport substrate.
 38. The optical module according to claim 1, furthercomprising a second conductive shield member, wherein the secondconductive shield member comprises a plurality of bonding wires.
 39. Theoptical module according to claim 38, wherein the linear wire and theplurality of bonding wires are made of gold.
 40. The optical moduleaccording to claim 38, wherein the linear wire and the plurality ofbonding wires comprise gold.
 41. The optical module according to claim38, wherein the linear wire and at least one of the plurality of bondingwires are disposed at approximately a same height.
 42. The opticalmodule according to claim 1, further comprising a driver IC, the driverIC being electrically connected to at least one of the at least twooptical elements.
 43. The optical module according to claim 42, furthercomprising an electric circuit substrate, wherein: the electric circuitsubstrate has a first surface, and the driver IC and the at least one ofthe at least two optical elements are disposed above the first surface.44. The optical module according to claim 43, wherein the at least twooptical elements comprise at least one light-emitting element and atleast one light-receiving element.
 45. The optical module according toclaim 44, wherein the electrical signal transmission paths comprise: afirst electrical signal transmission path connected to the at least onelight-emitting element; and a second electrical signal transmission pathconnected to the at least one light-receiving element.
 46. The opticalmodule according to claim 43, wherein the electric circuit substrate hasa ground electrode electrically connected to the first electrode. 47.The optical module according to claim 1, wherein the conductive shieldmember comprises a plurality of bonding wires aligned in substantially asame direction.
 48. The optical module according to claim 47, whereinthe plurality of bonding wires and at least one of the electrical signaltransmission paths are aligned in substantially a same direction. 49.The optical module according to claim 1, further comprising an opticalwaveguide member, wherein the optical waveguide member comprises a firstpath configured to propagate a first optical signal output from theoptical module.
 50. The optical module according to claim 49, wherein atleast one of the at least two optical elements is coupled to the firstpath via at least one reflective member.
 51. The optical moduleaccording to claim 49, wherein the optical waveguide member furthercomprises a second path configured to propagate a second optical signalinput to the optical module.
 52. The optical module according to claim51, wherein a portion of the first path and a portion of the second pathintersect.
 53. The optical module according to claim 51, wherein each ofone or more of the at least two optical elements is configured totransmit the first optical signal in a direction substantiallyperpendicular to a direction of the first path.
 54. The optical moduleaccording to claim 51, wherein each of one or more of the at least twooptical elements is configured to receive the second optical signal froma direction substantially perpendicular to a direction of the secondpath.